FreeNAS LogoWe've established that FreeNAS can mirror the USB flash drive boot device for redundancy. If one of them should fail, the system can be recovered with the other. I hadn't set out to verify the recovery procedure, but I stumbled into a practice run anyway. In hindsight it's good to get a feel of my recovery options now when I'm still playing with the system, rather than later when I'm in a panic to recover my data.

Over the past few days I've experimented with the boot volume, setting up the mirroring and using the built-in replacement mechanism to retire my USB sticks with checksum errors. After this was done, I unplugged the checksum-error drives (including the one I originally installed FreeNAS on) and rebooted the system.

It failed to boot and ended up at the GRUB recovery menu. Hmm, that's not good.

I plugged all the old drives back in... and that didn't improve the situation. Apparently, in the midst of all the mirroring and replacing, I managed to damage GRUB configuration so FreeNAS no longer boots.

Since I expected all the actual operating system files to be OK, I searched for a way to rebuild just the boot loader portion of the USB sticks. There are many ways to do this. The easiest - looking route I took is to perform an in-place upgrade.

I booted up the FreeNAS installation media, and selected the "Install/Upgrade" option. I pointed it to a USB drive that was free of checksum errors but would not boot. The installer detected an existing installation and offered to generate a new boot environment for the existing FreeNAS installation. Sounds perfect! I hit <OK>

Ten minutes later, the upgrade failed due to an error writing boot configuration files the installer wants to add. A quick Google search found a few suggestions on how to fix it using command-line tools I wasn't familiar with. I decided to try easier things first.

I restarted the installation process and chose the other upgrade option: An upgrade with a disk reformat rather than just generating a new boot environment. The installer will preserve a copy of the FreeNAS configuration but wipe everything else from scratch.

This approached was more destructive and took more time but it worked. My FreeNAS box booted back up as if nothing happened. Success!